Packaging film, packages and methods for using them

ABSTRACT

The invention provides a film, a package and methods for employing the same. The film has a first layer of an elastomer and a second layer of a polyethylene such as a single site catalyst polyethylene. The film can have a third layer of a polyethylene such that the second layer is disposed between the first and third layers. The polyethylene of the third layer also can be single site catalyst polyethylene and, the elastomer of the first layer can be styrene butadiene copolymer. The film has an oxygen transmission rate of up to about 1000, such as 150-450 cc/100 in 2  /24 hr., typically 260-400 cc/100 in 2  /24 hr., with values of 300, 350-360, 400 cc/100 in 2  /24 hr. and even higher exhibited by the film. The film is suitable for packages, for instance, packaging for cole slaw and leafy salad. The film also exhibits excellent clarity, durability, seal strength and machinability.

This application is a division of application Ser. No. 08/054,961, filedon Apr. 30, 1993, now U.S. Pat. No. 5,523,136.

FIELD OF THE INVENTION

The present invention relates to films and packages therefrom and tomethods for using them. The films have at least two layers including andelastomer layer such as butadiene styrene copolymer and a layer from asingle site catalyst polyethylene.

BACKGROUND OF THE INVENTION

Foods such as fresh, precut vegetables as a product in a package formedfrom film present unique problems. When living as part of a plant,vegetables absorb carbon dioxide from the atmosphere and release oxygen.However, when cut or picked from the plant, the vegetable tends toabsorb oxygen and release carbon dioxide (reverse photosynthesis). Thus,the nature of vegetables calls for packaging having certain permeabilitycharacteristics.

From health, safety and shelf-life perspectives, packaging for fresh,precut vegetables must have certain gas permeability characteristics.For instance, packaging for a leafy vegetable such as chopped cabbagewithout dressing (precut cole slaw) must have an oxygen transmissionrate (OTR) of about 300 to 400 cc/100 in² /24 hr. If precut vegetablesare in a package which has low permeability to gases such as oxygen(OTR), bacteria growth inside the package can be stimulated, which canspoil the vegetables. The bacteria can also grow undetected withoutmalodor or spoiling the food, and cause sickness. Further, thiscondition can lower the shelf-life of the vegetables. An approach toobtaining desired carbon dioxide and oxygen transmission through apackage is to provide the package with loose or open seals or,perforations. However, this approach literally leaves the food exposedto all possible contaminants, including bacteria, lowers the shelf-lifeof the food, and, to some extent, defeats the purpose of employingpackaging.

In addition, food such as fresh precut vegetables is an item which theconsumer prefers to visually inspect prior to purchasing, for instance,to see if the vegetables have spoiled. If the packaging is cloudy or notsufficiently transparent or translucent, the food is not especiallydesirable to the consumer. Likewise, the packaging should not be toosoft in order to provide adequate protection for the food. The packagingshould also be able to be sealed, such as by heat-sealing, with a sealwhich is sufficiently strong so as to also provide adequate protectionfor the food. Further, the packaging should not be constructed frommaterials having high levels of extractables because these materialstend to impart unpleasant odors or tastes to the food.

To meet the unique situation of vegetable packaging, it has beenproposed to use oriented polypropylene adhered by adhesive lamination topolyethylene. The polyethylene being heat-sealable allows the film to beformed into a package. Likewise, it has been proposed to coextrudeunoriented polypropylene and very low density polyethylene (VLDPE) andadhesively laminate the multi-layer coextrusion at the VLDPE side toanother layer of VLDPE. These types of structures however do not provideenhanced shelf life for vegetables with high respiration requirements;for instance, cole slaw, broccoli and cauliflower.

In particular, these packages do not exhibit sufficiently high orsufficiently consistently high OTR, or seal strength.

It has also been proposed to coextrude butadiene styrene as a core layerbetween two layers of polyethylene such as very low densitypolyethylene. However, this structure does not allow for resistant typecrimp seals as typically used in the snack food industry. The VLDPE isthe temperature-sensitive heat seal layer and, the butadiene styrene,which is more heat resistant, is in the core. Thus, the high temperatureheat sealing apparatus contacts the more temperature sensitive VLDPErather than the butadiene styrene. Accordingly, the seal temperaturemust be sufficiently low so as to prevent damage to the heat-sealableVLDPE layer contacting the heat-sealing apparatus resulting in a lowseal strength seal. In addition, such a structure can only be printedupon its outer surface, rendering the printing exposed to scuffing. Thepackage will therefore lose its label or be visually unappealing.Likewise, polyethylene such as linear low density polyethylene has beenused as a skin layer in an A/B/A film structure with another materialsuch as a copolymer of ethylene and an ethylenically unsaturatedcomonomer, for instance ethylene vinyl acetate (EVA), being the corelayer. This type of film structure can suffer from the disadvantages oflow seal strength because both outer layers are temperature sensitiveheat seal layers, and unpleasant odor or taste from the EVA.

However, characteristics such as heat sealability are not the onlycriteria by which one evaluates a film structure for suitability topackage food such as vegetables. Health and safety considerations arevery important. Thus, to obtain the desired OTR, certain films areadhered to a monolayer of polyethylene such as ultra linear low densitypolyethylene (ULDPE). However, films from these resins tend to be softand cloudy, rendering the film unsuitable with respect to appearance andlimiting its utility to impulse seals and not resistant seals.

Typically, polyethylene resins employed in packaging are low densitypolyethylene (LDPE), linear low density polyethylene (LLDPE), highdensity polyethylene (HDPE), VLDPE or ULDPE. These polyethylenes aretypically made with traditional Ziegler-type catalysts which containdifferent types of reaction sites which result in the polyethylenecontaining a broad range of molecules. For instance, the typicalpolyethylene contains polymers having medium molecular weight withmedium branching, low molecular weight with high branching, and highmolecular weight with low branching. This results in inconsistentproperties.

With respect to packaging materials, ecological considerations as wellas economic considerations make it desirable to have as few layers aspossible with the most favorable combination of properties. Inparticular, it would be desirable to have a two- or three-layeredstructure which has optimal clarity, optimal strength, can be readilyheat sealed, has a strong heat seal, can be readily printed upon, hasprotection for the printing, and, provides the proper barrier propertiesfor products such as vegetables.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a film which has anOTR of up to about 1000 such as about 150 to about 450, preferably about260-400, more preferably about 300-400 cc/100 in² /24 hr.

It is another object of the invention to provide a film which can beheat sealed and, which has a strong seal.

It is yet a further object of the invention to provide a film which issufficiently durable so as to be useful as a packaging material forfood, particularly leafy vegetables such as cole slaw and salad mix.

It is also an object of the invention to provide a film which hassufficient clarity so as to be useful as a packaging material for food.

It is additionally an object of the invention to provide a film whichcan be printed upon and, wherein the printing can be protected fromscuffing.

It is yet another object of the invention to provide a film having asfew layers as possible to obtain the desired combination of properties.

It is also an object of the invention to provide a package from a film.

And, it is an object of the invention to provide a method for packaginga product.

It has been surprisingly found that polyethylenes from a catalyst havingone type of catalytic site provide excellent properties with the respectto heat sealability and, oxygen and carbon dioxide transmission. It isfurther surprising that an elastomer such as butadiene styrene copolymercan be employed as an outer layer over such a single site catalystpolyethylene to provide a film which can meet the needs of the foodpackaging industry.

Thus, the present invention provides a film having oxygen permeabilityof up to about 1000, typically about 150-450 cc/100 in² /24 hr. The filmcomprises a first outer layer of an elastomer which is preferably heatresistant such as butadiene styrene copolymer and, a second layer of asingle site catalyst polyethylene. The film preferably has an oxygenpermeability of about 260-400 and, more preferably about 300-400 cc/100in² /24 hr.

The present invention also provides a coextruded film comprising a firstouter layer of butadiene styrene copolymer and, a second layer of singlesite catalyst polyethylene. In a preferred embodiment, the film includesa third layer of single site catalyst polyethylene which is adhesivelylaminated to the second layer. The three layer film can also includeprinting on the second or third layer.

The present invention also comprehends packages from the films of theinvention wherein the second or third layer is heat sealed. Theinvention further includes a method for packaging a product such asfood, preferably vegetables, more preferably, leafy vegetables such assalad or cole slaw, comprising sealing the product in a package madefrom the film. In addition, the invention comprehends a method forpreserving a product comprising storing the food in a package of theinvention.

BRIEF DESCRIPTION OF DRAWINGS

In the following detailed description reference will be made to theaccompanying drawings wherein:

FIG. 1 shows in cross-section a two layer film structure of theinvention;

FIG. 2 shows in cross-section a three layer film structure of thepresent invention;

FIG. 3 shows in cross-section a three layer structure of the presentinvention with printing;

FIG. 4 shows in cross-section a three layer structure of the presentinvention with printing; and,

FIG. 5 shows a package of the present invention.

DETAILED DESCRIPTION

Turning initially to the FIGS., FIGS. 1-4 show films 1-4 of theinvention. The films are shown in cross-section and, the thickness oflayers is arbitrary and not to necessarily represent the actualthickness of layers of the inventive film.

Film 1 of FIG. 1 is a two-layer structure comprised of layers 10 and 20.Layer 10 is an elastomer such as butadiene styrene and, layer 20 iscomprised of a single site catalyst polyethylene, which is discussed inmore detail below. Layers 10 and 20 can be joined by any suitable means.Co-extrusion is preferred.

FIG. 2 shows film 2 comprised of layers 10, 20 and 20' and, adhesive 25.Layers 10 and 20 are comprised of the same materials as layers 10 and 20of film 1 of FIG. 1 (hence the same numbering). Since layer 20' is alsocomprised of single site catalyst polyethylene but is a separate layer,it is numbered similarly to layer 20 of FIGS. 1 and 2, but is given theprime designation because it is a separate layer. In FIG. 2 layer 20 isbetween layers 10 and 20', with layer 20' having been separatelyextruded and, adhesive 25 adhering layers 20 and 20' to each other.

FIG. 3 shows three-layered film 3 which is akin to film 2 of FIG. 2,except that printing 22 is on the inner surface of layer 20, betweenlayer 20 and adhesive 25.

Film 4 of FIG. 4 is the same as film 3 of FIG. 3, except that the orderof the printing and adhesive are reversed. That is, printing 22 is onthe outer surface of layer 20', between layer 20' and adhesive 25.

FIG. 5 depicts package 5 of the invention wherein a sheet of film of theinvention is heat sealed at the periphery. Typically, portions of thesheet are brought into face-to-face relationship with layers 20 or 20'on each portion facing the opposing portion. Heat seals 28 are thenformed at or near the periphery to define an enclosed area. One side isleft open, as shown, for insertion of the product to be packaged and,the filled package is then closed and heat sealed along the open side.Heat seals 28 can be heat resistant type seals as found in snack foodpackaging.

Alternatively, the film may be made into a package by means of a form,fill and seal apparatus. For instance, the film can be formed into atube by forming a fin seal along opposing edges and, a transverse sealis also formed across the width of the tube (see, e.g., U.S. Pat. No.4,521,437, incorporated herein by reference). This process is suitablefor vertical form, fill and seal machines.

Package 5 of FIG. 5 can also contain resealing means positioned awayfrom a peripheral heat seal. For instance, slot means can be provided onone interior face and tab means on the opposing interior face of thepackage such that after the heat seal is cut away, the consumer canreseal the package by mating the tab with the slot. Such resealing meansor slot and tab means can be of the nature of the "zipper" or "zip-lock"type on existing plastic bags such as Dow's ZIPLOC™ or Illinois ToolWorks' ZIP PAK® food storage bags.

Turning to elastomer layer 10, this layer can be any suitableelastomeric polymer such as butadiene styrene copolymer,polymethylpentene, polybutylene, polyisobutylene, ethylene propylenediene monomer terpolymer, styrene butadiene styrene copolymer, styreneethylene butylene copolymer, styrene isoprene styrene copolymer,polybutene-1, isobutylene rubber, methyl acrylate butadiene styrenecopolymer, acrylonitrile butadiene styrene copolymer, acrylonitrilealkylacrylate butadiene styrene copolymer, methyl methacrylate alkylacrylate styrene copolymer, methyl methacrylate alkyl acrylate butadienestyrene copolymer, and the like. Considerations for selecting a materialfor layer 10 include sufficient heat resistance, OTR, strength andclarity.

Butadiene styrene copolymer is a presently preferred elastomer for layer10. Preferred butadiene styrene copolymers are those of the K-Resin®series from Phillips 66, e.g., KR03, KR04, KR05 and KR10. Of these, KR05is preferred and, its normal physical properties are set forth below inTable 1.

                  TABLE 1                                                         ______________________________________                                        NOMINAL PHYSICAL PROPERTIES                                                   OF KR05 SB COPOLYMER**                                                                   ENGLISH      SI                                                    PROPERTY ASTM    UNIT     VALUE   UNIT   VALUE                                ______________________________________                                        Density  D792    g/cc     1.01    g/cc   1.01                                 Flow Rate,                                                                             D1238   g/10 min 8.0     g/10 min                                                                             8.0                                  Condition G                                                                   Tensile Yield                                                                          D638                                                                 Strength                                                                      2 in (50 mm)     %        160     %      160                                  per min*                                                                      Flexural D790    psi      205,000 MPa    1413                                 Modulus*                                                                      Flexural Yield                                                                         D790    psi      4900    MPa    34                                   Strength*                                                                     Heat Deflection                                                                        D638                                                                 Temperature                                                                   264 psi          °F.                                                                             163     °C.                                                                           73                                   (1.8 MPa)                                                                     Fiber Stress                                                                  Izod Impact                                                                            D256                                                                 Strength                                                                      1/8 in (3.2 mm)  ft-lbf/in                                                                              0.75    J/m    41                                   Specimen                                                                      Hardness,                                                                              D2240            65             65                                   Shore D                                                                       Vicat Softening                                                                        D1525   °F.                                                                             188     °C.                                                                           87                                   Point                                                                         Light    --      %        90      %      90                                   Transmission                                                                  Moisture D570    %        0.09    %      0.09                                 Absorption,                                                                   24 h                                                                          ______________________________________                                         *Specimen injection molded by ASTM Method D1897.                              **From Product Literature                                                

Other elastomeric materials exhibiting substantially similar propertiesor suitable heat resistance, OTR, strength and clarity characteristicscan be employed for layer 10 and, one can sacrifice clarity if visualappearance and inspection of the packaged product is not a majorconsideration.

As to layers 20 and 20', metallocene catalyst systems are utilized forproducing polyethylenes such as those described in U.S. Pat. Nos.4,808,561, 4,871,705, 4,871,523, 4,897,455, 4,925,821, 4,935,397,4,937,301, 4,952,714, 5,001,205, 5,001,244, 5,006,500, 5,013,803,5,017,655, 5,026,798, 5,032,652, 5,077,255, 5,079,205, 5,084,534,5,124,418, and 5,183,867, each of which is hereby incorporated herein byreference. Metallocene catalysts tend to have one type of reaction site,as opposed to traditional Zeigler-type catalysts which have differenttypes of reaction sites. Polyethylenes from Zeigler-type catalysts arepolymers containing a broad range of molecules. Polyethylenes fromcatalysts having one type of reaction site have been found to be moreconsistent and exhibit superior properties over conventionalpolyethylenes. Polyethylene polymers from a catalyst having one type ofreaction site are herein termed "single site catalyst polyethylene" and,are commercially available from Exxon Chemical as "EXACT™" products suchas EXACT™ 2009, 2010, 3001, 3006, 3016, 3025, 3026, 3027, 3028 and,4011. Presently EXACT™ 3025 and EXACT™ 3028 are preferred single sitecatalyst polyethylenes. Typical properties for the single site catalystpolyethylenes EXACT™ 3025 and EXACT™ 3028 (from Exxon Chemical ProductLiterature) are set forth in Tables 2 and 3, below.

                  TABLE 2                                                         ______________________________________                                        EXACT ™ 3025 (LINEAR ETHYLENE-BASED COPOLYMER)                                           ASTM                TYPICAL                                     POLYMER PROPERTIES                                                                          METHOD     UNITS    VALUE                                       ______________________________________                                        Melt Index    D-1238 (E) dg/min   1.2                                         Density       D-792      g/cm     0.910                                       DSC Peak Melting Point                                                                      Exxon Method                                                                             °C.                                                                             103                                         Film Properties.sup.1,2                                                       1% Secant Modulus                                                                           D-882      psi (MPa)                                            MD                                16900 (117)                                 TD                                18000 (124)                                 Tensile Strength @ Yield                                                                    D-882      psi (MPa)                                            MD                                980 (6.8)                                   TD                                930 (6.4)                                   Tensile Strength @ Break                                                                    D-882      psi (MPa)                                            MD                                8140 (56)                                   TD                                5680 (39)                                   Elongation @ Break                                                                          D-882      %                                                    MD                                640                                         TD                                660                                         Elmendorf Tear Strength                                                                     D-1922     g/mil                                                MD                                111                                         TD                                237                                         Dart Drop Impact; F.sub.50                                                                  D-1709     g/mil    >1050                                       Puncture,                                                                     Force         Exxon Method                                                                             lbs/mil  5.9                                         Energy                   in-lbs/mil                                                                             14.3                                        Total Energy Impact                                                                         D-4272     ft-lbs                                               @ 23° C.                   2.1                                         @ -29° C.                  1.7                                         Haze          D-1003     %        3.7                                         Gloss         D-2457     %        79                                          ______________________________________                                         .sup.1 1.25 mil film produced on a 2.5' blown film line with 2:1 BUR, mel     temperature between 380-415° F., and throughout of 8 lbs/hr/in die     .sup.2 Films contain 500 PPM slip and 2000 PPM antiblock.                

                  TABLE 3                                                         ______________________________________                                        EXACT ™ 3028 (LINEAR ETHYLENE-BASED COPOLYMER)                                           ASTM                TYPICAL                                     POLYMER PROPERTIES                                                                          METHOD     UNITS    VALUE                                       ______________________________________                                        Melt Index    D-1238 (E) dg/min   1.2                                         Density       D-792      g/cm     0.900                                       DSC Peak Melting Point                                                                      Exxon Method                                                                             °C.                                                                             92                                          Film Properties.sup.1,2                                                       1% Secant Modulus                                                                           D-882      psi (MPa)                                            MD                                10600 (73)                                  TD                                10800 (74)                                  Tensile Strength @ Yield                                                                    D-882      psi (MPa)                                            MD                                660 (4.6)                                   TD                                610 (4.2)                                   Tensile Strength @ Break                                                                    D-882      psi (MPa)                                            MD                                8670 (60)                                   TD                                7250 (50)                                   Elongation @ Break                                                                          D-882      %                                                    MD                                590                                         TD                                680                                         Elmendorf Tear Strength                                                                     D-1922     g/mil                                                MD                                123                                         TD                                177                                         Dart Drop Impact; F.sub.50                                                                  D-1709     g/mil    >1058                                       Puncture,                                                                     Force         Exxon Method                                                                             lbs/mil  7                                           Energy                   in-lbs/mil                                                                             21                                          Total Energy Impact                                                                         D-4272     ft-lbs                                               @ 23° C.                   >6.2                                        @ -29° C.                  2.2                                         Haze          D-1003     %        3.1                                         Gloss         D-2457     %        83                                          ______________________________________                                         .sup.1 1.25 mil film produced on a 2.5' blown film line with 2:1 BUR, mel     temperature between 380-415° F., and throughout of 8 lbs/hr/in die     .sup.2 Films contain 500 PPM slip and 2000 PPM antiblock.                

The EXACT™ 3025 and 3028 are copolymers of ethylene and 1-butene and arelinear ethylene polymers which are unique types of very low densitypolyethylenes. These single site polyethylenes have a narrow molecularweight distribution, typically greater than 1,000 and less than 100,000and, a narrow range of single chain branching of about 12 or 12.5 toabout 30 SCB/1000 carbons. Single site catalyst polyethylenes have anabsence of low molecular weight, high comonomer content molecules, anabsence of high molecular weight, low comonomer molecules, a narrowmolecular weight distribution with slightly lower melt strength thantraditional linear polymers and, a slightly flatter shear rate viscositycurve. Single site polyethylenes are a preferred material for a layer 20or 20' of the film of the present invention. Other suitable materialscan be employed for layer 20 or 20' if the material exhibits similarproperties to the preferred single site catalyst polyethylene or, theresultant film displays the desired seal strength and OTRcharacteristics. For instance, other single site catalyst polyethyleneswhich can be used for layer 20 or 20' include Exxon's Exact™ and Exxpol™resins as well as Dow's Insite™ resin. The use of single site catalystpolyethylene as a layer provides distinct advantages such as moreconsistency in OTR. For example, films including polypropylene haveexperienced wide swings in OTR: if the thickness of the polypropylenelayer varies by 0.1 mil, then a 20% variation in OTR may be observedand, this is not a tolerable variation in the packaging industry.

Adhesive layer 25 can be any suitable adhesive to laminate thecoextrusion comprising layers 10 and 20 to layer 20' such as solvent orliquid adhesive, e.g., water-based or urethane adhesive, or solidadhesive. The adhesive should not detract from the desiredcharacteristics of the film. Preferred adhesives for layer 25 aresolventless adhesives such as the TYCEL® laminating adhesives availablefrom the Lord Corporation, e.g., the TYCEL® 7975 Adhesive and TYCEL®7276 curing agent.

Printing 22 can be imparted to the film by flexographic or rotogravureapparatus, with the ink employed preferably being suitable for foodpackaging. Referring to FIG. 1, printing can be placed upon the outerexposed or inner surface of layer 10 or, the surface of layer 20 whichis in contact with layer 10.

The film of the invention can be any suitable thickness. Thickness canbe varied depending upon the end use for the film. Typical thicknessesmay range from about 3 microns to about 0.030 inches (0.25 mm) for athin film to about 1 to 2 mm if a thick film is desired. With referenceto FIGS. 1-4, layer 10 is typically about 0.5 to 2.0 mils thick,preferably about 1.0 to 1.5 mils thick. Layers 20 and 20' are typicallyabout 0.1 to about 1.5 mils thick. Accordingly, films 1 to 4 aretypically about 0.6 to about 3.5 mils thick, preferably about 1 to 3mils thick and, more preferably about 2 to 2.5 mils thick. The film canbe supplied to users in a rollstock format for automatic form, fill andseal equipment or, it can be made into preformed bags or pouches (seeFIG. 5).

The film of the invention is especially useful for packaging food suchas precut produce, for instance, lettuce, cabbage, salad mixes, coleslaw mix, potatoes, onions and other vegetables and fruits, especiallythose which tend to respire. For washing and cooling produce and fordetermining and controlling the proper modified or unmodified packagingatmosphere for perishables such as produce, reference is made to U.S.Pat. Nos. 4,996,071 and 4,962,777, incorporated herein by reference.However, the invention is not necessarily limited by the productcontained within a package made from the inventive film as the film cansuitably be used whenever a "breathable" package is desired. However,the inventive film is especially useful for packaging food productswhich tend to oxidize because these foods require packaging having anOTR of about 260-400 cc/100 in² /24 hr. Indeed, in packaging from theinventive film, cole slaw and leafy salads have an excellent shelf-lifeof about 4 to about 6 weeks. The inventive film exhibits OTRs of up to1000 and from 150-450, typically 260-450, such as 300, 350 and 400cc/100 in² /24 hr. Furthermore, the inventive film and packagestherefrom exhibit excellent clarity and seal strength. Thus, theinventive film and packages are suitable for the food service industry(e.g., hospitals, schools, restaurants, fast food, etc.) whereappearance and seal strength are especially important and, longshelf-life may be required.

While coextrusion is preferred for forming film 1 (FIG. 1) and, adhesivelamination is preferred for adhering layer 20' to layer 20 (films 2-4;FIGS. 2-4), the films of the present invention can manufactured by anysuitable means. With reference to FIGS. 1-4, layers 10, 20 and 20' maybe joined by coextrusion, lamination, extrusion lamination and the like.

Further, while the invention has been illustrated with respect to two-and three-layer films, additional layers may be present. However, it isdesirable that the films exhibit the permeability (OTR values) of theillustrated and exemplified two- and three-layer films. Likewise, ifadditional layers are present, the outer layer (layer 10 in FIGS. 1-4)should be from a heat resistant elastomer and, the innermost layershould be a heat sealable polymer, preferably a polyethylene and, mostpreferably a single site catalyst polyethylene. Thus, between layers 10and 20, between layers 20 and 20' or between both layers 10 and 20 andlayers 20 and 20' can be an additional layer or layers from any suitablematerial such as polyethylene, LDPE, LLDPE, ULDPE, VLDPE, HDPE,polypropylene, oriented polypropylene, single site catalystpolyethylene, an elastomer (such as those mentioned above for layer 10or other commercially available materials such as ethylene-propylene andethylene-butene copolymer elastomers), or blends thereof. However, giventhe excellent performance of the two- and three-layer films of theinvention and economic and ecological considerations, additional layersare not considered necessary.

The following non-limiting Examples are given by way of illustrationonly and are not to be considered a limitation of this invention.

EXAMPLES EXAMPLE 1 THREE-PLY FILM

A three-ply A/B/B film according to the invention was made bycoextruding the A/B layers (A=butadiene styrene, KR05; B=EXACT™ 3025single site catalyst polyethylene) and, adhesively laminating thecoextruded structure to the separately extruded third "B" layer(Adhesive laminate=TYCEL® 7925 and 7276). The coextruded structure had a1.3 mil total thickness comprised of 1 mil butadiene styrene and 0.3 milsingle site catalyst polyethylene. The inner film had a 1.2 milthickness. The total structure 2.5 mil had a thickness and had an oxygentransmission rate of 160 cubic centimeters per one hundred square inchesin a twenty four hour period.

EXAMPLE 2 THREE-PLY FILM

A three-ply A/B/B film according to the invention was made bycoextruding the A/B layers (A=butadiene styrene, KR05; B=EXACT™ 3028single site catalyst polyethylene) and, adhesively laminating thecoextruded structure to the separately extruded third "B" layer(Adhesive laminate=TYCEL® 7975 and 7276). The coextruded structure hadabout a 1 mil thickness comprised of 0.7 mil butadiene styrene and about0.2 mil single site catalyst polyethylene. The innermost "B" film had a1 mil thickness. The total structure had a 2 mils thickness and had anoxygen transmission rate of 360 cubic centimeters per one hundred squareinches in a twenty-four hour period.

EXAMPLE 3 THREE-PLY FILM

A three-ply A/B/B film according to the invention was made bycoextruding the A/B layers (A=butadiene styrene, KR05; B=EXACT™ 3025single site catalyst polyethylene) and, adhesively laminating thecoextruded structure to the separately extruded third "B" layer(Adhesive laminate=TYCEL® 7975 and 7276). The coextruded structure hadabout a 1 mil thickness comprised of 0.7 mil butadiene styrene and about0.3 nil single site catalyst polyethylene. The innermost "B" film had a1.2 mil thickness. The total structure had a 2.2 mils thickness and hadan oxygen transmission rate of 250 cubic centimeters per one hundredsquare inches in a twenty-four hour period.

Each of Examples 1-3 utilized butadiene styrene and single site catalystpolyethylene, but, the polyethylenes varied in density, effecting theoxygen transmission rates. By further varying the density of the singlesite catalyst polyethylene and/or changing the heat resistant layer(layer 10 in FIGS. 1-4), for instance to polymethylpentene, the films ofthe invention can achieve OTR values up to 1000, for instance, in the800-1000 cc/100 in² /24 hr range for products such as broccoli,cauliflower and the like and, in the 600-700 cc/100 in² /24 hr range forpackaging of product such as baby carrots (see Example 5).

EXAMPLE 4 TWO-PLY FILM

A two-ply A/B film according to the invention was made by coextrudingthe A/B layers (A=butadiene styrene, KR05; B=EXACT™ 3028). Each layerwas about 1.0 mil thick and, the film had a total thickness of about 2.0mil. The film had an oxygen transmission rate of about 340 cubiccentimeters per one hundred square inches in a twenty-four hour period.

EXAMPLE 5 HIGH OTR TWO-PLY FILM

A two-ply A/B film according to the invention is made by coextrudingpolymethylpentene (as the A layer) and single site catalyst polyethylene(as the B layer). The film is about 1.25 mil thick and, respires in the1000 cc/100 in² /24 hr range.

EXAMPLE 6 PACKAGING UTILITY

Film as per Example 2 was formed into packages with form, fill and sealapparatus and, a comparative film having an A/B/B structure (wherein theA/B layers were a coextrusion and the third "B" layer was adhesivelylaminated to the second "B" layer (A=unoriented polypropylene; B=VLDPE))was also formed into packages with form, fill and seal apparatus. Thecomparative film was also about 2 mil total thickness with the third "B"layer about 1 mil thick and, the A/B coextrusion was about 1 mil thick(A≅0.3; B≅0.7 mil).

The packages were filled with one pound shredded cabbage or, 8 ouncesof: broccoli florets; or cauliflower florets; or vegetable blends. Thecomparative film and the packages therefrom had an OTR of about 220cc/100 in² /24 hr whereas the inventive film and packages therefromexhibited OTR approximately in accordance with Example 2 (about 350-360cc/100 in² /24 hr). The packages from the inventive film and cabbage,broccoli, cauliflower and vegetable blends therein were acceptable: thecabbage, broccoli, cauliflower and vegetable blends exhibitedsatisfactory characteristics associated with sufficient oxygentransmission, e.g., no foul odor.

The cabbage, broccoli, cauliflower and vegetable blends packaged in thepackage from the comparative film exhibited unsatisfactory qualitycharacteristics associated with low package oxygen levels, e.g., foulodor. Thus, the ultimate product (packaged cabbage, broccoli,cauliflower, vegetable blend or vegetables in general) was notacceptable; and accordingly, the comparative film was not acceptable forthis utility. The ultimate product and its acceptability dependeddirectly on the OTR characteristics of the film of the package.

Indeed, produce such as broccoli requires a package having an OTR of atleast 300 cc/100 in² /24 hr. The approximately 39% lower OTR of thecompetitive film (0.39×360≅220) was unsuitable and unacceptable as werepackages and ultimate products (the cabbage, broccoli, cauliflower andvegetables) therefrom. The high OTR of the inventive film allows it tobe used for packaging products requiring high respiration requirementssuch as certain vegetables, e.g., broccoli, cauliflower, cole slaw andthe like and, it can also be used for lower transmission products likeRomaine lettuce.

For fresh produce items having high respiration requirement, such ascabbage, broccoli and cauliflower, and various blends of suchvegetables, the packages from the inventive film as per Example 2demonstrated OTR characteristics which provided an acceptable ultimateproduct, i.e., without causing the critical odor quality defectsassociated with insufficient oxygen in the package. As the produce itemrespired in the package, oxygen was consumed; the film OTR of theinventive film was the package characteristic which permitted new oxygeninto the package at a rate sufficient to maintain the equilibrium oxygenlevel required for a good quality product inside the package. Theinventive film exhibited sufficiently high OTR to prevent production ofthe foul odors associated with anaerobic respiration. The comparativefilm failed to achieve an acceptable ultimate product (one without foulodor). Thus, the inventive film provided a package and an ultimateproduct therein which was acceptable and of good quality whereas thecompetitive film failed to achieve such.

EXAMPLE 7 MACHINABILITY

A film as per Example 2 was formed into a package with form, fill andseal apparatus. The package contained 1 lb. cole slaw mix. The jaw sealwas resistance type and, the seam seal was fin type. The web width was173/8 inches. The film and package were tested on a scale of "poor","fair", "good", "very good" and "excellent" for the followingcharacteristics (with rating also provided):

    ______________________________________                                        CHARACTERISTIC          RATING                                                ______________________________________                                        End Seal -- Heat & Dwell Range                                                                        Excellent                                             End Seal Integrity      Excellent                                             Seam Seal -- Heat & Dwell Range                                                                       Excellent                                             Seam Seal Integrity     Excellent                                             Bottom End Seal Speed 50 bpm                                                                          Excellent                                             Seal Thru Wrinkles -- End Seam                                                                        Excellent                                             Seal Thru Wrinkles -- Seam Seal                                                                       Excellent                                             ______________________________________                                    

The package was also leak tested (evaluated for seal integrity, sealstrength and stress handling) by submerging it in a vaccuum chamber, andwas "ok" (no leak) at 15", 20" and 23" vacuum (the latter being themaximum of the chamber). The film was overall rated as excellent, veryuser friendly, with no wrinkles in the side seam, very minor wrinkles inthe end seals, nice clarity and, excellent sealability. The inventivefilm is very machinable and, can overcome prior art seal problems, whileproviding a package having desired OTR, strength and appearancecharacteristics.

A utility of the inventive film is packaging for produce items with highoxygen requirements, especially on form, fill and seal apparatus such ashigh speed form-fill seal (FFS) equipment. Key characteristics of theinventive film which make it uniquely capable of achieving this utility(objective) are related to the multilayer laminate film structurecombined with the high oxygen transmission rate (OTR) of the film.

The laminated construction of the inventive film provides FFS machinecharacteristics which permitted high operating speeds along with bagseals of high strength and integrity (resistance seals). Thus, theultimate product e.g., packaged vegetables, can be produced at costeffective line speeds with a very low incidence of package seal failure.The inventive film was tested and found to be the only laminate filmwhich can be resistance sealed in this manner and supply the necessaryOTR required for ultimate products, e.g., packaged vegetables, ofquality (see Example 6). The inventive film therefore provides the freshproduce industry with the ability to economically produce packagedvegetables, especially vegetables with high oxygen transmissionrequirements, in packages with resistance seals.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. A method for packaging a product comprising heatsealing a film so as to form a package, said film comprisinga firstouter layer comprising styrene-butadiene copolymer and a second layercomprising a single site catalyst polyethylene, wherein said film has anoxygen transmission rate of about 150-450 or greater up to about 1000cc/100 in² /24 hr. and can be sealed with resistance seals or on a form,fill, and seal machine.
 2. The method of claim 1 wherein the productrequires oxygen.
 3. The method of claim 2 wherein said product comprisesa leafy vegetable.
 4. The method of claim 3 wherein said leafy vegetableis lettuce or cabbage.
 5. A method of preserving a food productcomprising storing the food product in a package formed by heat sealinga film, said film comprisinga first outer layer comprisingstyrene-butadiene copolymer and a second layer comprising a single sitecatalyst polyethylene, wherein said film has an oxygen transmission rateof about 150-450 or greater up to about 1000 cc/100 in² /24 hr. and canbe sealed with resistance seals or on a form, fill, and seal machine. 6.The method of claim 5, wherein the food product is selected from thegroup consisting of cabbage and lettuce.
 7. The method of claim 6wherein said cabbage is in the form of cole slaw mix.
 8. The method ofclaim 1 wherein said film has an oxygen transmission rate of from about260 to about 400 cc/100 in² /24 hr.
 9. The method of claim 1 whereinsaid film has an oxygen transmission rate of about 300 cc/100 in² /24hr.
 10. The method of claim 1 wherein said film has an oxygentransmission rate of from about 350 to about 360 cc/100 in² /24 hr. 11.The method of claim 1 wherein said film has an oxygen transmission rateof about 400 cc/100 in² /24 hr.
 12. The method of claim 1 wherein thefirst and second layers of said film are in intimate contact with eachother.
 13. The method of claim 1 wherein the first and second layers ofsaid film are coextruded.
 14. The method of claim 13 wherein said firstand second layers are in intimate contact with each other.
 15. Themethod of claim 1 wherein said film further comprises a third layercomprising single site catalyst polyethylene, said second layer beingdisposed between said first and third layers.
 16. The method of claim 15wherein said first and second layers are coextruded and said third layeris adhesively laminated to said second layer.
 17. The film of claim 16further comprising printing on said second or third layer.
 18. Themethod of claim 5 wherein said film has an oxygen transmission rate offrom about 260 to about 400 cc/100 in² /24 hr.
 19. The method of claim 5wherein said film has an oxygen transmission rate of about 300 cc/100in² /24 hr.
 20. The method of claim 5 wherein said film has an oxygentransmission rate of from about 350 to about 360 cc/100 in² /24 hr. 21.The method of claim 5 wherein said film has an oxygen transmission rateof about 400 cc/100 in² /24 hr.
 22. The method of claim 5 wherein thefirst and second layers of said film are in intimate contact with eachother.
 23. The method of claim 5 wherein the first and second layers ofsaid film are coextruded.
 24. The method of claim 23 wherein said firstand second layers are in intimate contact with each other.
 25. Themethod of claim 5 wherein said film further comprises a third layercomprising single site catalyst polyethylene, said second layer beingdisposed between said first and third layers.
 26. The method of claim 25wherein said first and second layers are coextruded and said third layeris adhesively laminated to said second layer.
 27. The film of claim 26further comprising printing on said second or third layer.